Physiological sensor

ABSTRACT

A sensor used to measure physiological characteristics of body tissues is provided. The physiological sensor includes a first light source assembly having a first light source in parallel with a second light source. Each of the first light source and the second light source have an anode and a cathode. A second light source assembly includes a third light source in parallel with a fourth light source. Each of the third light source and the fourth light source have an anode and a cathode. The anode of the first light source is electrically connected to the cathode of the second light source, the anode of said third light source, and the cathode of said fourth light source. The anode of the third light source is electrically connected to the cathode of the fourth light source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/755,432, filed Jan. 31, 2013, entitled “PHYSIOLOGICAL SENSOR”, whichis a continuation of U.S. application Ser. No. 11/963,174, filed Dec.21, 2007, now U.S. Pat. No. 8,380,272, entitled “PHYSIOLOGICAL SENSOR”,issued Feb. 19, 2013, which are incorporated herein by reference intheir entirety.

BACKGROUND

To improve the accuracy of the measurement, or to enable the measurementof additional physiological characteristics, additional wavelengths oflight can be used. This generally necessitates the addition of lightsources requiring additional wires to carry the excitation potentials.Unfortunately, the addition of wires adds to the cost and complexity ofthe system. Moreover, monitoring systems are generally configured towork with sensor pads having a fixed number of wires. For example, if amonitoring system is configured to work with sensor pads having a threewire configuration, a sensor pad using additional light sources andhaving any more than three wires may not be compatible with the existingmonitoring system.

One known method used to minimize the number of wires in a sensor padwhen increasing the number of light sources includes having multiplelight sources connected in a matrix of rows and columns of wires. Thelight sources in this configuration are activated by sequentiallyaddressing the row and column of each light source with an excitationpath. In this way, four wires provide connection and activation of fourlight sources. If pairs of light sources are connected in parallel, thesame configuration of four wires can be used to connect and activate upto eight light sources. This configuration, however, requires a minimumof four wires and is limited to a maximum of eight light sources.

Accordingly, the embodiments described hereinafter were developed inlight of these and other drawbacks associated with increasing the numberof light sources in a physiological sensor without increasing the numberof wires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary physiological sensoraccording to an embodiment;

FIG. 2 is a bottom view of a pad of the physiological sensor, accordingto an embodiment;

FIG. 3 is a bottom view of the physiological sensor according to anotherembodiment with multiple light source locations;

FIG. 4 is a bottom view of the physiological sensor according to thirdembodiment with multiple light source locations;

FIG. 5 is a bottom view of a physiological sensor having a plurality ofsensing pads;

FIG. 6 is a block diagram illustrating an exemplary control scheme,according to an embodiment;

FIG. 7 is a diagram illustrating an exemplary control circuit and lightassembly, according to an embodiment;

FIG. 8 is a diagram illustrating another exemplary control circuit andlight assembly, according to an embodiment;

FIG. 9 is a diagram illustrating another exemplary control circuit andlight assembly, according to an embodiment;

FIG. 10 is a diagram illustrating the exemplary control circuit andlight assembly as set forth in FIG. 9 having multiple current sources;and

FIG. 11 is a diagram illustrating another exemplary control circuit andlight assembly, according to an embodiment.

DETAILED DESCRIPTION

A physiological sensor that allows for an increased number of lightsources without an increase in the number of wires is provided.Specifically, the physiological sensor can use four or six light sourcesin a three-wire configuration, or alternatively, up to twelve lightsources in a four-wire configuration. In either embodiment, thephysiological sensor includes one or more light source assemblieselectrically connected to a monitoring system and in opticalcommunication with at least one light detector. Each light sourceassembly includes at least one light source.

The arrangement of the light sources allows the physiological sensor tomeasure physiological characteristics of body tissue such as oxygensaturation or other various hemoglobin species with increased accuracyand without a significant increase in size or cost. The arrangement ofthe light sources may also measure concentrations of additionalchromospheres in tissue besides hemoglobin. The spatial relationship ofthe light sources relative to the light detector may enhance spatialresolution and provide values at different depths, which may help inorgan oxygen delivery monitoring.

Moreover, because the physiological sensor maintains a three or fourwire configuration, the physiological sensor may be used withpre-existing monitoring systems, thus making the physiological sensordescribed herein backwards compatible. It is to be understood that thephysiological sensor may be configured to work with any number of wiressince the number of light assemblies (each having two light sources) isrelated to the number of wires. Specifically, the number of light sourceassemblies can be calculated by the equation: N_(LSA)=N_(W)*(N_(W)−1)/2,wherein N_(LSA) is the number of light source assemblies and N_(W) isthe number of wires.

FIG. 1 illustrates an exemplary physiological sensor system 10 thatincludes a monitoring system 12 connected to a sensor pad 14 through acable 16. As best shown in FIG. 2, the sensor pad 14 includes aplurality of light sources 18 in optical communication with first andsecond light detectors 20, 22. It is to be appreciated that multiplelight sources 18 may be disposed in multiple openings of the sensor pad14. The plurality of light sources 18 may include any light source knownin the art, including but not limited to, light emitting diodes, laserdiodes or any combination thereof. Typically, the frequency of the lightexcitation and wavelength of the light source is dependent upon theapplication. For instance, in cerebral oximetry, pulse oximetry, ortissue oximetry applications, the light sources 18 may have a wavelengthin the visible and/or infrared spectrum. For instance, the light sources18 may have a wavelength between 600 nm and 1000 nm, including, but notlimited to, a wavelength of 660 nm, 724 nm, 750 nm, 770 nm, 812 nm, 850nm, 905 nm, or any combination thereof. It is to be understood that thelight sources 18 may have other wavelengths to measure otherphysiological characteristics.

As shown in FIGS. 3 and 4, the plurality of light sources 18 may bemounted in two or more different physical locations on the sensor pad 14or in openings in the pad 14. By adding additional light sourceassemblies when the physiological sensor system 10 is used as a cerebraloximeter sensor, the monitoring system 12 can obtain additionalabsorption spectra at additional wavelengths. The additional absorptionspectra can help to better define the extinction curves for variousblood and tissue chromophores, allowing more accurate determination oftheir relative concentrations. In one embodiment, each light source 18is illuminated sequentially and independently, allowing measurement oflight absorption at specific wavelengths by one or more of the lightdetectors 20, 22. Alternatively, two or more light sources 18 may beilluminated simultaneously to provide additional light output and animproved signal-to-noise ratio at specific wavelengths. This may benecessary because certain wavelengths of light do not penetrate asdeeply into tissue as other wavelengths do. As will be discussed ingreater detail below, illuminating several light sources 18simultaneously may include multiple current sources. Alternatively,certain light sources may not have the same light output as others.Simultaneously illuminating two or more of these lower output lightsources can increase the effective light output, improvingsignal-to-noise ratio and stability.

In another embodiment, the physiological sensor system 10 may be usedfor fractional oximetry to measure fractional oxygen saturation andadditional hemoglobin species in deep tissue of the brain, other organs,skin, or in skeletal muscle tissue. By selecting wavelengths of lightappropriately, additional fractional concentrations of other hemoglobinspecies such as carboxyhemoglobin and methemoglobin can be determined.Most noninvasive oximeters measure functional hemoglobin oxygensaturation, which is defined as the ratio of oxyhemoglobin to theunbound hemoglobin that is available for oxygen binding. As such, itdoes not measure or take into effect the proportion of hemoglobin thatis bound to other compounds such as carbon monoxide (carboxyhemoglobin)or hydrogen sulfide (sulfhemoglobin). Additional species of hemoglobinsuch as methemoglobin, where the ferrous iron has been oxidized toferric iron, are not measured either. By incorporating additionalwavelengths of light, the effect of additional chromophores with uniqueextinction curves can be measured, enabling estimation of the fractionof each hemoglobin compound, or fractional saturation.

In yet another embodiment, some of the plurality of light sources 18 maybe used for cerebral or tissue oximetry and others of the plurality oflight sources 18 may be used for pulse oximetry to measure arterialblood hemoglobin oxygen saturation. This allows the physiological sensorsystem 10 to measure various physiological characteristics with the samesensor pad 14. In this embodiment, a first light source assembly 44 mayuse selected wavelengths of light and be located a sufficient distancefrom one of the detectors 20, 22 to measure cerebral oxygen saturationwhile a second light source assembly 46 may use wavelengths suited formeasurement of arterial oxygen saturation using reflectance pulseoximetry and would therefore be located close to another of the lightdetectors 20, 22. Alternatively, the first light detector 20 may be usedto measure arterial oxygen saturation based on the spatial relationshipof the plurality of light sources 18. This embodiment also allowsarterial saturation of deeper tissues to be measured because the depthof penetration of photons is proportional to the separation distancebetween the light source 18 and the light detector 20, 22.

In yet another embodiment, the plurality of light sources 18 can bespatially arranged to increase the accuracy of the measurements. Forinstance, the first light source assembly 44 can have differentwavelengths that penetrate less deeply into the body tissue than otherlight source assemblies. For instance, as shown in FIG. 3, placing thefirst light source assembly 44 closer to the light detector 20 andslightly offset from the first light source assembly 46 allows the firstlight source assembly 44 to penetrate into the body tissue shallowerthan the second light source assembly 46. Likewise, placing the secondlight source 46 further away from the light detector 20 and slightlyoffset from the first light source assembly 44 causes light generated bythe second light source assembly 46 to penetrate deeper into the bodytissue. Alternatively, as shown in FIG. 4, the first light sourceassembly 44 may be spaced away from the second light source assembly 46and more offset from the second light source assembly 46 to achieve asimilar result. In this embodiment, the ratios of the signals from eachof the light detectors 20, 22 can be computed using both light sourceassemblies 44, 46.

In yet another embodiment, the physiological sensor system 10 maycontain a plurality of sensor pads 14 and each sensor pad 14 may containat least one light source assembly 44 and one light detector 20. Thisarrangement of the physiological sensor system 10 may be used to measuretwo physiological parameters including, but not limited to, cerebralblood saturation and arterial blood saturation. The cerebral measurementmay require a low skin perfusion site on the forehead to reduceinterference from extra-cranial signals. However, arterial blood oxygensaturation may require high skin perfusion. Thus, in one embodiment, forcerebral oximetry, the sensor pad 14 may be placed on the foreheaddirectly below the hair line. On the other hand, for pulse oximetry, thesensor pad 14 may be placed on the forehead directly above the eyes. Inthis embodiment, a single sensor pad 14 may be inconvenient to use atleast for an adult patient. Therefore, two sensor pads 14 may be used.

Referring now to FIG. 5, in one exemplary approach, the physiologicalsensor system 10 includes a first sensor pad 14A and a second sensor pad14B. The first sensor pad 14A may be used, for instance, for tissueoximetry, and the second sensor pad 14B may be used, for instance, forpulse oximetry. The first sensor pad 14A may include the light sourceassemblies 44, 46, in optical communication with the first and secondlight detectors 20, 22. It is to be appreciated that the first sensorpad 14A may include any number of light source assemblies 44, 46 and anynumber of light detectors 20, 22. Likewise, the second sensor pad 14Bmay include the light source assemblies 44, 46, in optical communicationwith the first and second light detectors 20, 22. It is to beappreciated that the second sensor pad 14B may include any number oflight source assemblies 44, 46 and any number of light detectors 20, 22.

Other cases where two or more sensor pads 14 may be used includemeasuring cerebral oxygenation from at least two sites of the brain, ormeasuring cerebral and tissue oxygenation simultaneously in infants. Inthis embodiment, the physiological sensor system 10 may include at leasttwo sensor pads 14, each having at least two light detectors 20, 22 andat least two light source assemblies 42, 46. The light source assemblies42, 46 may be connected as described above and excited sequentially intime.

As shown in FIG. 6, monitoring system 12 includes a control circuit 24and a processor 26 in communication with the plurality of light sources18 and light detectors 20, 22. The processor 26 is configured to receivesignals from light detectors 20, 22 and converts the signals into datathat indicates the physiological characteristics of the body tissue.Furthermore, the processor 26 controls the control circuit 24 as will bediscussed in greater detail below. It is to be understood that thecontrol circuit 24 may alternatively be controlled by a dedicatedprocessor (not shown) other than the processor 26 shown in FIG. 6. Themonitoring system 12 may output the data to a display 27 as shown inFIG. 1.

FIG. 7 illustrates an exemplary control circuit 24, which includes atleast one high switch 28 and at least one low switch 30. As discussed ingreater detail below, it is to be understood that the high switch 28connects the light sources 18 to a higher potential than the low switch30. The high switch 28 and the low switch 30 may be any switch known inthe art, and even the same type of switch. For instance, the high switch28 and the low switch 30 may be transistors. In one embodiment, the highswitch 28 may be a PMOS type transistor and the low switch 30 may be anNMOS type transistor. The high switch 28 and the low switch 30 may beconnected in an H-Bridge configuration.

The at least one high switch 28 and the at least one low switch 30 arecontrolled by the processor 26 in the monitoring system 12. In otherwords, the processor 26 opens and closes the at least one high switch 28and the at least one low switch 30 of the control circuit 24 to activatea select combination of the plurality of light sources 18. Themonitoring system 12 includes a voltage source 32 electrically connectedto the control circuit 24 for providing voltage to the control circuit24 and the plurality of light sources 18. In addition, the monitoringsystem 12 may further include a current source 34 that causes current toflow from the voltage source 32 to ground 36. The low switches 30connect each of the plurality of light sources 18 to the current source34. The current source 34 is connected to the ground 36 at a groundpotential. It is to be understood that the low switches 30 may connectto the plurality of light sources 18 directly to the ground potential.Otherwise, in at least one embodiment, there is no structural orfunctional difference between the high switches 28 and the low switches30.

The control circuit 24 may include any number of high switches 28 or lowswitches 30. For instance, as shown in FIG. 7, the control circuit 24includes a first high switch HI1 in series with a first low switch L1,the combination of which defines a first switch pair 38. Likewise, thecontrol circuit 24 includes a second high switch HI2 in series with asecond low switch L2, the combination of which defines a second switchpair 40. It is to be understood that the control circuit 24 may includeany number of high switches 28 and low switches 30 to define any numberof switch pairs. For instance, referring to FIG. 8, the control circuit24 may include a third high switch HI3 and a third low switch L3 inseries with the third high switch HI3 to define a third switch pair 42.As shown in FIG. 8, the first switch pair 38 is in parallel with thesecond switch pair 40 and the third switch pair 42.

Each high switch 28 and each low switch 30 have an anode and a cathode.The anode of the high switch 28 directly or indirectly connects to thevoltage source 32 and the cathode of the low switch 30 directly orindirectly connects to a lower potential (i.e., a ground potential 36 orthe current source 34). When the control circuit 24 includes multiplehigh switches 28, the anodes of each of the high switches 28 areelectrically connected to one another. For example, referring to FIG. 7,the anode of the first high switch HI1 may be electrically connected tothe anode of the second high switch HI2. Similarly, when the controlcircuit 24 includes multiple low switches 30, the cathodes of each ofthe low switches 30 may be electrically connected. Again referring toFIG. 7, the cathode of the first low switch L1 is electrically connectedto the cathode of the second low switch L2.

In operation, the processor 26 closes one of the high switches 28 andone of the low switches 30 to activate one of the plurality of lightsources 18. In one embodiment, each light source is connected to twoswitch pairs. The light source is powered by the voltage source 32 whenthe high switch 28 in one of the switch pairs is closed and the lowswitch 30 in another switch pair is closed, completing an electricalcircuit. It is to be understood that multiple light sources may beilluminated by closing more than one high switch 28 and/or more than onelow switch 30. However, closing the high switch 28 and the low switch 30in the same switch pair will cause an electrical short, and the lightsource will not illuminate. In other words, the light source does notoperate when the high switch 28 and the low switch 30 from the sameswitch pair are both closed. To prevent an electrical short, theprocessor 26 opens the low switch 30 in the switch pair when the highswitch 28 in the switch pair is closed. Therefore, the light source iselectrically connected to the high switch 28 in one switch pair and thelow switch 30 in another switch pair. It is to be understood that boththe high switch 28 and the low switch 30 may be open at the same time.

As shown in FIG. 7, the physiological sensor 10 includes a first lightsource assembly 44 that is defined by at least one of the plurality oflight sources 18 and electrically connected to the control circuit 24.As shown, the first light source assembly 44 includes a first lightsource LS1 in parallel with a second light source LS2. As previouslydiscussed, the first light source LS1 and the second light source LS2may be light emitting diodes or laser diodes. Each of the first lightsource LS1 and the second light source LS2 have an anode and a cathode.The anode of the first light source LS1 is electrically connected to thecathode of the second light source LS2. In addition, the cathode of thefirst light source LS1 is electrically connected to the anode of thesecond light source LS2. Therefore, although disposed in parallel withthe second light source LS2, the first light source LS1 has an oppositepolarity to the second light source LS2. The first light source LS1 andthe second light source LS2 are each electrically connected to at leasttwo switch pairs. Specifically, the first light source LS1 iselectrically connected to the first high switch HI1 and the second lowswitch L2, and the second light source LS2 is electrically connected tothe second high switch HI2 and the first low switch L1. The first highswitch HI1 is in series with the second low switch L2 when the firsthigh switch HI1 and the second low switch L2 are closed. Likewise, thesecond high switch HI2 is in series with the first low switch L1 whenthe second high switch HI2 and the first low switch L1 are closed. Inthis embodiment, only one of the plurality of light sources 28 may beilluminated at any time since only one of the first high switch HI1 andthe second high switch HI2 may be closed because closing both the firsthigh switch HI1 and the first low switch L1 or the second high switchHI2 and the second low switch L2 would cause an electrical short.Therefore, the processor 26 opens the first low switch L1 when the firsthigh switch HI1 is closed. Likewise, the processor 26 opens the secondlow switch L2 when the second high switch HI2 is closed.

It is to be understood that the physiological sensor system 10 mayinclude any number of light source assemblies. For instance, referringto FIG. 8, the system 10 further includes a second light source assembly46 defined by at least one of the plurality of light sources 18 andelectrically connected to the monitoring system 12. The second lightsource assembly 46 includes a third light source LS3 in parallel with afourth light source LS4. Although disposed in parallel with the fourthlight source LS4, the third light source LS3 has an opposite polaritythan the fourth light source LS4. Each of the third light source LS3 andthe fourth light source LS4 have an anode and a cathode. The anode ofthe third light source LS3 is electrically connected to the cathode ofthe fourth light source LS4. The cathode of the third light source LS3is electrically connected to the anode of the fourth light source LS4.In one embodiment, as shown in FIG. 8, the anode of the third lightsource LS3 is also electrically connected to the anode of the firstlight source LS1 and the cathode of the second light source LS2. As inthe previous embodiment, the first light source LS1 is electricallyconnected to the first high switch HI1 and the second low switch L2 andthe second light source LS2 is electrically connected to the second highswitch HI2 and the first low switch L1. In this embodiment, the thirdlight source LS3 is electrically connected to the first high switch HI1and the third low switch L3. The fourth light source LS4 is electricallyconnected to the third high switch HI3 and the first high switch HI1.Again, the third high switch HI3 is in series with the third low switchL3 to make up the third switch pair 42.

In this embodiment, it is possible for the processor 26 to illuminatemore than one of the plurality of light sources 18 simultaneously. Forinstance, the processor 26 may close the first high switch HI1 and thesecond low switch L2 to illuminate the first light source LS1. Theprocessor 26 may then close the third low switch L3 to illuminate thethird light source LS3 since both the first light source LS1 and thethird light source LS3 receive power from the voltage source 32 when thefirst high switch HI1 is closed. It is to be appreciated that theprocessor 26 may close the third low switch L3 at the same time asclosing the second low switch L2 to illuminate the third light sourceLS3 simultaneously with the first light source LS1, or the processor 26may close the third low switch L3 after closing the second low switch L2to illuminate the third light source LS3 sequentially with the firstlight source LS1. Alternatively, the processor 26 may close the secondhigh switch HI2 and the first low switch L1 to illuminate the secondlight source LS2, and by closing the third high switch HI3 while thesecond high switch HI2 and the first low switch L1 are closed, theprocessor 26 additionally illuminates the fourth light source LS4.Therefore, in this embodiment, the processor 26 may illuminate two ofthe plurality of light sources 18.

Referring now to FIG. 9, the physiological sensor system 10 furtherincludes a third light source assembly 48 that includes a fifth lightsource LS5 in parallel with a sixth light source LS6. Although disposedin parallel with the sixth light source LS6, the fifth light source LS5has an opposite polarity than the sixth light source LS6. Each of thefifth light source LS5 and the sixth light source LS6 have an anode anda cathode. The anode of the fifth light source LS5 is electricallyconnected to the cathode of the first light source LS1, the anode of thesecond light source LS2, and the cathode of the sixth light source LS6.The cathode of the fifth light source LS5 is electrically connected tothe cathode of the third light source LS3, the anode of the fourth lightsource LS4, and the anode of the sixth light source LS6. The anode ofthe sixth light source LS6 is electrically connected to the cathode ofthe third light source LS3 and the anode of the fourth light source LS4.The cathode of the sixth light source LS6 is electrically connected tothe cathode of the first light source LS1 and the anode of the secondlight source LS2. As in the previous embodiment, the processor 26 mayilluminate more than one of the plurality of light sources 18simultaneously. For instance, the processor 26 may close the first highswitch HI1 and the second low switch L2 to illuminate the first lightsource LS1. At the same time, the processor 26 may close the third lowswitch L3 to illuminate the third light source LS3. Therefore, theprocessor 26 may illuminate more than one of the plurality of lightsources 18 simultaneously.

In one exemplary embodiment, to illuminate more than one of theplurality of light sources 18 simultaneously, the physiological sensorsystem 10 may include more than one current sources 34. Referring now toFIG. 10, the physiological sensor 10 includes a first current source 34Aelectrically connected to the first low switch L1, a second currentsource 34B electrically connected to the second low switch L2, and athird current source 34C electrically connected to the third low switchL3. The current sources 34A, 34B, and 34C help to ensure that the lightsources 18 maintain a minimum amount of brightness when the lightsources 18 are simultaneously illuminated.

Again, it is to be understood that the physiological sensor system 10may include any number of light source assemblies. For instance,referring to FIG. 11, the physiological sensor system 10 furtherincludes a fourth light source assembly 50, a fifth light sourceassembly 54, and a sixth light source assembly 56. In addition, thecontrol circuit 24 includes a fourth switch pair 52 having a fourth highswitch HI4 in series with a fourth low switch L4. The fourth lightsource assembly 50 includes a seventh light source LS7 in parallel withan eighth light source LS8. The seventh light source LS7 and the eighthlight source LS8 each have an anode and a cathode. The anode of theseventh light source LS7 is electrically connected to the fourth highswitch HI4 and the cathode of the seventh light source LS7 iselectrically connected to the third ground 36 source. The anode of theeighth light source LS8 is electrically connected to the third highswitch HI3 and the cathode of the eighth light source LS8 iselectrically connected to the fourth low switch L4. The fifth lightsource assembly 54 includes a ninth light source LS9 in parallel with atenth light source LS10. The ninth light source LS9 and the tenth lightsource LS10 each have an anode and a cathode. The anode of the ninthlight source LS9 is electrically connected to the fourth high switch HI4and the cathode of the ninth light source LS9 is electrically connectedto the second low switch L2. The anode of the tenth light source LS10 iselectrically connected to the second high switch HI2 and the cathode ofthe tenth light source LS10 is electrically connected to the fourth lowswitch L4. The sixth light source assembly 56 includes an eleventh lightsource LS11 in parallel with a twelfth light source LS12. The eleventhlight source LS11 and the twelfth light source LS12 each have an anodeand a cathode. The anode of the eleventh light source LS11 iselectrically connected to the fourth high switch HI4 and the cathode ofthe eleventh light source LS11 electrically connected to the first lowswitch L1. The anode of the twelfth light source LS12 is electricallyconnected to the first high switch HI1 and the cathode of the twelfthlight source LS12 is electrically connected to the fourth low switch L4.As in the previous embodiments, the processor 26 may illuminate one ormore of the plurality of light sources 18. For instance, the processor26 may close the first high switch HI1, the second low switch L2, andthe fourth low switch L4 to illuminate the first light source LS1, thethird light source LS3, and the twelfth light source LS12.Alternatively, the processor 26 may close the first high switch HI1, thethird high switch HI3, the fourth high switch HI4, and the second lowswitch L2 to illuminate the first light source LS1, the sixth lightsource LS6, and the ninth light source LS9.

It is to be understood that the physiological sensor system 10 mayinclude any number of light source assemblies, each including any numberof light sources 18. Also, the processor 26 may close differentcombinations of the high switches 28 and the low switches 30 toilluminate alternative combinations of the plurality of light sources18.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many alternative approaches orapplications other than the examples provided would be apparent to thoseof skill in the art upon reading the above description. The scope of theinvention should be determined, not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. It is anticipated and intended that futuredevelopments will occur in the arts discussed herein, and that thedisclosed systems and methods will be incorporated into such futureexamples. In sum, it should be understood that the invention is capableof modification and variation and is limited only by the followingclaims.

The present embodiments have been particularly shown and described,which are merely illustrative of the best modes. It should be understoodby those skilled in the art that various alternatives to the embodimentsdescribed herein may be employed in practicing the claims withoutdeparting from the spirit and scope as defined in the following claims.It is intended that the following claims define the scope of theinvention and that the method and apparatus within the scope of theseclaims and their equivalents be covered thereby. This description shouldbe understood to include all novel and non-obvious combinations ofelements described herein, and claims may be presented in this or alater application to any novel and non-obvious combination of theseelements. Moreover, the foregoing embodiments are illustrative, and nosingle feature or element is essential to all possible combinations thatmay be claimed in this or a later application.

All terms used in the claims are intended to be given their broadestreasonable constructions and their ordinary meanings as understood bythose skilled in the art unless an explicit indication to the contraryis made herein. In particular, use of the singular articles such as “a,”“the,” “said,” etc. should be read to recite one or more of theindicated elements unless a claim recites an explicit limitation to thecontrary.

1. A system, comprising: a first light source assembly disposed on asensor pad at a first location, wherein the first light source assemblycomprises a first plurality of light sources configured to emit lightinto a body tissue; a first detector spaced a first distance apart fromthe first light source assembly on the sensor pad, wherein the firstdetector is configured to detect the emitted light; a second detectorspaced a second distance apart from the first light source assembly onthe sensor pad along an imaginary axis connecting the first light sourceassembly and the first detector, wherein the second detector isconfigured to detect the emitted light, and wherein the first lightsource assembly, the first detector, and the second detector areconfigured for cerebral or tissue oximetry; and a second light sourceassembly disposed on the sensor pad at a second location, wherein thesecond location is offset from the imaginary axis and closer to thefirst and second detectors than the first location, wherein the secondlight source assembly comprises a second plurality of light sourcesconfigured to emit light into the body tissue, and wherein the secondlight source assembly and one or both of the second detectors areconfigured for pulse oximetry.
 2. The system of claim 1, wherein thefirst light source assembly is configured to emit one or morewavelengths of light suitable for cerebral or tissue oximetry deeperinto the body tissue than the second light source assembly.
 3. Thesystem of claim 1, wherein the imaginary axis intersects a sensor cablecoupled to the sensor pad.
 4. The system of claim 1, wherein the secondlocation of the second light source assembly is above the imaginary axisand closer to a first edge of the sensor pad than the first light sourceassembly.
 5. The system of claim 1, wherein a distance between the firstand second detectors is less than the first distance.
 6. The system ofclaim 3, wherein the sensor cable couples the first and second lightsource assemblies and the first and second detectors to a monitoringdevice.
 7. The system of claim 6, wherein the monitoring devicecomprises a plurality of current sources, and wherein at least onecurrent source of the plurality of current sources is electricallycoupled to at least one light source of the first and second pluralityof light sources.
 8. The system of claim 6, wherein the monitoringdevice is configured to activate one or more light sources of the firstand second plurality of light sources.
 9. The system of claim 1, whereinat least one of the first light source assembly and the second lightsource assembly comprises a light emitting diode and a laser diode. 10.A sensor, comprising: at least one sensor pad; a first light sourceassembly disposed on the sensor pad at a first location, wherein thefirst light source assembly comprises a first plurality of light sourcesconfigured to emit light into a body tissue; a first detector spaced afirst distance apart from the first light source assembly on the sensorpad, wherein the first detector is configured to detect the emittedlight; a second detector spaced a second distance from the first lightsource assembly on the sensor pad, wherein the second distance isgreater than the first distance, and wherein the second detector isconfigured to detect the emitted light; and a second light sourceassembly disposed on the sensor pad at a second location, wherein thesecond location is farther from the first and second detectors than thefirst location, and wherein the second location is offset from animaginary axis intersecting the first location, the first detector, andthe second detector, and wherein the second light source assemblycomprises a second plurality of light sources configured to emit lightinto the body tissue.
 11. The sensor of claim 10, wherein the firstlight source assembly, the first detector, and the second detector areconfigured for cerebral or tissue oximetry.
 12. The sensor of claim 10,wherein the second light source assembly and one or both of the firstdetector and the second detector are configured for pulse oximetry. 13.The sensor of claim 10, wherein the first light source assembly emitsone or more wavelengths of light deeper into the tissue body than thesecond light source assembly.
 14. The sensor of claim 10, wherein theimaginary axis is parallel to a largest edge of the sensor pad.
 15. Thesensor of claim 10, wherein at least one of the first light sourceassembly and the second light source assembly comprise a light emittingdiode and a laser diode.
 16. The sensor of claim 10, wherein the sensorpad is configured to be applied to a forehead of a patient.
 17. Amethod, comprising: driving one or more light sources of a first lightsource assembly disposed on a sensor pad at a first location, whereinthe one or more light sources of the first light source assembly areconfigured to emit light into a body tissue; receiving one or more firstsignals from one of a first detector or a second detector disposed onthe sensor pad, wherein the one or more first signals are related to anamount of light detected by the first or second detector from the firstlight source assembly, and wherein the one or more first signals areassociated with pulse oximetry monitoring; driving one or more lightsources of a second light source assembly disposed on a sensor pad at asecond location, wherein the second location is farther from the firstand second detectors than the first light source assembly, and whereinthe one or more light sources of the second light source assembly areconfigured to emit light into a body tissue; receiving one or moresecond signals from the first detector and the second detector, whereinthe one or more second signals are related to an amount of lightdetected from the second light source assembly, and wherein the one ormore second signals are associated with cerebral or tissue oximetrymonitoring.
 18. The method of claim 17, comprising determining anarterial blood saturation of the body tissue based at least in part onthe one or more first signals.
 19. The method of claim 17, comprisingdetermining a cerebral blood saturation of the body tissue based atleast in part on the one or more second signals.
 20. The method of claim17, comprising driving the one or more light sources of the first andsecond light source assemblies sequentially.